When tensile forces are applied to textile structures consisting of twisted, interwoven, interlooped, or entangled fibers, local deformations will often consist of a combination of tensile, bending, lateral compression and surface shearing, and unbending modes.The static-loop test combines the first three of these deformation modes, the sliding or dynamic-loop test adds the last two modes and readily lends itself to fatigue testing. The current paper reports on observations of filament deformation and fracture incurred during both static and dynamic-loop tests in contrast to what occurs during straight tensile tests. The damage processes observed include: opening of tensile cracks at surface flaws, catastrophic tensile failure, fiber flattening, coupled shear bands due to axial compression, surface shingling due to extreme shearing, gross filament distortion due to ploughing, crack branching accompanied by longitudinal splitting, surface wear, abrasion, and cutting. As expected, fibers with different tensile properties exhibit different combinations of deformation and fracture modes; likewise, different modes are manifested in the same fiber when testing is conducted at room condition and in liquid nitrogen.

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It is generally accepted that inducing molecular alignment in a polymer precursor via mechanical stresses influences its graphitization during pyrolysis. However, our understanding of how variations of the imposed mechanics can influence pyrolytic carbon microstructure and functionality is inadequate. Developing such insight is consequential for different aspects of carbon MEMS manufacturing and applicability, as pyrolytic carbons are the main building blocks of MEMS devices. Herein, we study the outcomes of contrasting routes of stress-induced graphitization by providing a comparative analysis of the effects of compressive stress versus standard tensile treatment of PAN-based carbon precursors. The results of different materials characterizations (including scanning electron microscopy, Raman and X-ray photoelectron spectroscopies, as well as high-resolution transmission electron microscopy) reveal that while subjecting precursor molecules to both types of mechanical stresses will induce graphitization in the resulting pyrolytic carbon, this effect is more pronounced in the case of compressive stress. We also evaluated the mechanical behavior of three carbon types, namely compression-induced (CIPC), tension-induced (TIPC), and untreated pyrolytic carbon (PC) by Dynamic Mechanical Analysis (DMA) of carbon samples in their as-synthesized mat format. Using DMA, the elastic modulus, ultimate tensile strength, and ductility of CIPC and TIPC films are determined and compared with untreated pyrolytic carbon. Both stress-induced carbons exhibit enhanced stiffness and strength properties over untreated carbons. The compression-induced films reveal remarkably larger mechanical enhancement with the elastic modulus 26 times higher and tensile strength 2.85 times higher for CIPC compared to untreated pyrolytic carbon. However, these improvements come at the expense of lowered ductility for compression-treated carbon, while tension-treated carbon does not show any loss of ductility. The results provided by this report point to the ways that the carbon MEMS industry can improve and revise the current standard strategies for manufacturing and implementing carbon-based micro-devices.

Use of thermoplastic olefin elastomers (TPO) is expected to enjoy a 12% annual growth worldwide through 1996. The majority of growth is in automotive applications such as bumper fascia, claddings, exterior panels, airbag covers and instrument panels, etc. This healthy forecast is fueled by the overall cost/performance, the wide range of properties available, the ease of processing and the recyclability of this class of material. The current TPO business is dominated by compounded grades which offer: freedom in formulation to meet specific customer needs, good balance of physical properties, minimal dimensional change during processing, and flexibility to incorporate colors and other additives for tailored applications.In compounding, the dispersion and distribution of polymer phases as well as fillers and additives can be controlled through mixing. This article discusses the methodology involved in studying the effect of mixing on the performance of TPO formulations with different filler levels in a laboratory scale intensive batch mixer. Variables studied are mix time and batch size. Properties analyzed include heat elongation, tear strength, mold shrinkage, melt flow rate, density and cold temperature impact. The behavior of these compounds is graphically illustrated using a statistical software package. The results, in general, suggest an optimal mix time of around three minutes for most of the Downloaded from 323 systems evaluated. It is theorized that through intensive mixing, phase morphology is changed and fillers are also preferentially incorporated into selected polymer phases to provide reinforcement. Electron microscopy and a low strain rheology technique are used to confirm some of these observations. Results on experimentation with single screw and twin screw extruders are also discussed. The variables studied in the extruders are barrel temperature and screw speed. Impact and flexural properties of different TPO formulations are compared for the three different types of mixing processes.

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